The present invention relates to an optical system for scanning and more particularly to an optical system which is able to control the angle of field for scanning.
Hitherto, such type of optical system is known in which a beam for scanning is twice deflected in order that the angle of scanning field made by the first deflection may be different from that made by the second deflection. An example of such type of optical system is disclosed in U.S. Pat. No. 3,771,850.
In the scanning optical system disclosed in this patent specification, the first deflecting mirror is the same as the second one. More particularly, the scanning optical system is so designed that the beam deflected by the first deflecting mirror is directed to an afocal optical system and the deflected beam issued from it is reflected by a stationary mirror disposed in the vicinity of the focal plane of the rear lens group of the afocal optical system toward the latter. The deflected beam re-issued from the afocal optical system is again directed into the same first deflecting mirror.
This arrangement of scanning optical system does not allow control of the angle of deviation of the deflected beam finally obtained and the beam system.